create box for number in flutter code example

Example: squared text field flutter

new TextFormField(
                      decoration: new InputDecoration(
                        labelText: "Enter Email",
                        fillColor: Colors.white,
                        border: new OutlineInputBorder(
                          borderRadius: new BorderRadius.circular(25.0),
                          borderSide: new BorderSide(
                          ),
                        ),
                        //fillColor: Colors.green
                      ),
                      validator: (val) {
                        if(val.length==0) {
                          return "Email cannot be empty";
                        }else{
                          return null;
                        }
                      },
                      keyboardType: TextInputType.emailAddress,
                    ),